Re: A Data Object in Cocoa
Re: A Data Object in Cocoa
- Subject: Re: A Data Object in Cocoa
- From: "Michael Ash" <email@hidden>
- Date: Sat, 10 Jan 2009 12:18:16 -0500
On Sat, Jan 10, 2009 at 12:08 PM, Alastair Houghton
<email@hidden> wrote:
> On 10 Jan 2009, at 16:48, Michael Ash wrote:
>
>> As for underscore being reserved, I have never been able to figure out
>> any consequence of a conflict with an Apple ivar name. It may cause
>> your source to fail to compile, but it won't cause any *binary*
>> compatibility problems, which is the real menace.
>
> I *think* the problem here is introspection... if you subclass an Apple
> provided class and add an instance variable with the same name as one of
> theirs, it's possible that any of the dynamic mechanisms the frameworks (or,
> for that matter, your own code) use to get the value of an object property
> might use the wrong variable, with unexpected results.
Not using an underscore won't save you here. Mechanisms like KVC will
look for ivars both with and without the underscore. In fact, leaving
off the underscore makes things worse: with the underscore, the
compiler will at least error when you try to recompile later on,
whereas without it the conflict will exist silently.
A cow-orker just pointed out to me that Apple does not, in fact,
recommend against an underscore prefix for instance variables. They do
recommend against them for private methods, but that's a completely
different question. It seems that the well-known recommendation
against _ivars is actually a misconception! If I'm wrong and just
missed it, I'd like to know where it says so. But no trace of such a
recommendation in Coding Guidelines for Cocoa: Naming Instance
Variables and Data Types:
http://developer.apple.com/DOCUMENTATION/Cocoa/Conceptual/CodingGuidelines/Articles/NamingIvarsAndTypes.html#//apple_ref/doc/uid/20001284
Mike
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden